1. Field of the Invention
The invention relates to a method of measuring exhaust gas of internal combustion engines, preferably in test benches, through the use of CVS (constant value sampling) full-flow systems whereby the exhaust gas of the internal combustion engine is mixed with combustion gas, preferably air, and whereby the volume flow or mass flow of the combustion air is determined by the CVS full-flow system and whereby the maximum quantity of combustion air needed by the internal combustion engine is thereby exceeded. The invention relates further to a device to carry out the method of measuring exhaust gas of internal combustion engines, preferably exhaust gas measurement in test benches, through the use of CVS full-flow systems.
2. The Prior Art
The condition of the intake air influences the operational behavior of an internal combustion engines to a large degree. Since the development of internal combustion engines have placed increasingly higher requirements relative to the reproducibility and accuracy of test results, and based on exhaust gas regulations becoming more stringent worldwide as well as the higher power density, it is therefore necessary to eliminate all influences as much as possible which would influence the test results in the development of engines. Since the condition of the intake air is included in these influences, it is necessary to condition this intake air to achieve comparable test conditions at the test bench. The atmospheric pressure is a significantly influencing value specifically for certification whereby testing systems have been known to be problem cases for already a long time relative to unfavorable geodetic and climatic situations.
Known systems for conditioning of intake air for internal combustion engines are commercially available (e.g. the Combustion Air Conditioning Unit of AVL List GmbH, Graz/Austria or FEV AirCon of FEV Motorentechnik GmbH, Aachen/Germany). However, these systems are directly connected to the air supply system of the internal combustion engine and they must follow in this way the changes of the operating condition of the internal combustion engine and the resulting change of airflow rate, and these systems must also follow thereby directly the changes of the rate of airflow of the internal combustion engine itself. During rapid and dynamic changes of air flow in the engine, as described in general also in DE 40 15 818 C2, these changes can be followed only to a limited degree so that only a poor quality of adjustment can be achieved during the dynamic changes in the rate of airflow.
PCT/AT01/00371 describes a device and a method whereby a reliable and constant conditioning of the combustion air can be ensured even under highly dynamic operational conditions in which essentially a constant and fully conditioned quantity of the combustion gas is provided at each instant which corresponds to at least the maximum quantity required by the respective internal combustion engine. Through this measure, conditioning does not have to be performed again dynamically since the engine on the test bench has branches in the supply line for the maximal required quantity of combustion air diverting the quantity of combustion air need for the actual respective operating conditions. The conditioning system disposed upstream has to be designed nevertheless for the maximum quantity of combustion air whereby a constant mass flow passes through the conditioning passage in the case of the invention whereby control is made correspondingly simple.
According to a variant of AT 6824 U2 is was proposed that the volume flow or mass flow of the combustion gas is adjusted downstream from the internal combustion engine to avoid possible pulsations of the entire adjustment system and to considerably increase the adjustment dynamics so that changes in set values can be performed very rapidly with the least possible influence on the entire adjustment system. A set value for the apparatus is determined thereby as a defined function of the atmospheric pressure, the desired set pressure value, and the characteristic of the apparatus so that the set pressure value can be determined upstream from the internal combustion engine from the actual value of the set value of the apparatus through a defined function whereby the actual set pressure value is adjusted upstream from the internal combustion engine.
However, systems are now required which are suitable to be used together with CVS full-flow systems at increased control dynamics without large effects on the entire adjustment system whereby dilution of the engine exhaust gases must be avoided upstream of this CVS full-flow system. Systems with rapid pressure control circuits currently proposed for this purpose, which maintain the intake air condition nearly constant, do not offer the desired quality of control and conditioning.